scholarly journals Bjerknes-like Compensation in the Wintertime North Pacific

2015 ◽  
Vol 45 (5) ◽  
pp. 1339-1355 ◽  
Author(s):  
Stuart P. Bishop ◽  
Frank O. Bryan ◽  
R. Justin Small
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
Western Boundary ◽  
Meridional Heat Transport ◽  
Western Boundary Currents ◽  
Boundary Currents ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific ◽  
Kuroshio Extension Region

AbstractObservational and model evidence has been mounting that mesoscale eddies play an important role in air–sea interaction in the vicinity of western boundary currents and can affect the jet stream storm track. What is less clear is the interplay between oceanic and atmospheric meridional heat transport in the vicinity of western boundary currents. It is first shown that variability in the North Pacific, particularly in the Kuroshio Extension region, simulated by a high-resolution fully coupled version of the Community Earth System Model matches observations with similar mechanisms and phase relationships involved in the variability. The Pacific decadal oscillation (PDO) is correlated with sea surface height anomalies generated in the central Pacific that propagate west preceding Kuroshio Extension variability with a ~3–4-yr lag. It is then shown that there is a near compensation of O(0.1) PW (PW ≡ 1015 W) between wintertime atmospheric and oceanic meridional heat transport on decadal time scales in the North Pacific. This compensation has characteristics of Bjerknes compensation and is tied to the mesoscale eddy activity in the Kuroshio Extension region.

scholarly journals On the Relationship between Synoptic Wintertime Atmospheric Variability and Path Shifts in the Gulf Stream and the Kuroshio Extension

2009 ◽  
Vol 22 (12) ◽  
pp. 3177-3192 ◽  
Author(s):  
Terrence M. Joyce ◽  
Young-Oh Kwon ◽  
Lisan Yu
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Western Boundary ◽  
Atmospheric Variability ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Coherent, large-scale shifts in the paths of the Gulf Stream (GS) and the Kuroshio Extension (KE) occur on interannual to decadal time scales. Attention has usually been drawn to causes for these shifts in the overlying atmosphere, with some built-in delay of up to a few years resulting from propagation of wind-forced variability within the ocean. However, these shifts in the latitudes of separated western boundary currents can cause substantial changes in SST, which may influence the synoptic atmospheric variability with little or no time delay. Various measures of wintertime atmospheric variability in the synoptic band (2–8 days) are examined using a relatively new dataset for air–sea exchange [Objectively Analyzed Air–Sea Fluxes (OAFlux)] and subsurface temperature indices of the Gulf Stream and Kuroshio path that are insulated from direct air–sea exchange, and therefore are preferable to SST. Significant changes are found in the atmospheric variability following changes in the paths of these currents, sometimes in a local fashion such as meridional shifts in measures of local storm tracks, and sometimes in nonlocal, broad regions coincident with and downstream of the oceanic forcing. Differences between the North Pacific (KE) and North Atlantic (GS) may be partly related to the more zonal orientation of the KE and the stronger SST signals of the GS, but could also be due to differences in mean storm-track characteristics over the North Pacific and North Atlantic.

“Eddy Resolving” Observation of the North Pacific Subtropical Mode Water

2011 ◽  
Vol 41 (4) ◽  
pp. 666-681 ◽  
Author(s):  
Eitarou Oka ◽  
Toshio Suga ◽  
Chiho Sukigara ◽  
Katsuya Toyama ◽  
Keishi Shimada ◽  
...  
Keyword(s):  
High Resolution ◽  
North Pacific ◽  
Kuroshio Extension ◽  
Uniform Structure ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Late Fall ◽  
The Kuroshio ◽  
The North Pacific

Abstract Hydrographic data obtained by high-resolution shipboard observations and Argo profiling floats have been analyzed to study the mesoscale structure and circulation of the North Pacific Subtropical Mode Water (STMW). The float data show that in the late winter of 2008, STMW having a temperature of approximately 18.8°, 17.7°, and 16.6°C formed west of 140°E, at 140°–150°E, and east of 150°E, respectively, in the recirculation gyre south of the Kuroshio Extension. After spring, the newly formed STMW gradually shift southward, decreasing in thickness. Simultaneously, the STMWs of 16.6° and 17.7°C are gradually stirred and then mixed in terms of properties. In late fall, they seem to be integrated to form a single group of STMWs having a temperature centered at 17.2°C. Such STMW circulation in 2008 is much more turbulent than that in 2006, which was investigated in a previous study. The difference between the two years is attributed to the more variable state of the Kuroshio Extension in 2008, associated with stronger eddy activities in the STMW formation region, which enhance the eddy transport of STMW. High-resolution shipboard observations were carried out southeast of Japan at 141°–147°E in the early fall of 2008. To the south of the Kuroshio Extension, STMW exists as a sequence of patches with a horizontal scale of 100–200 km, whose thick portions correspond well to the mesoscale deepening of the permanent pycnocline. The western (eastern) hydrographic sections are occupied mostly by the 17.7°C (16.6°C) STMW, within which the 16.6°C (17.7°C) STMW exists locally, mostly at locations where both the permanent pycnocline depth and the STMW thickness are maximum. This structure implies that the STMW patches are transported away from their respective formation sites, corresponding to a shift in the mesoscale anticyclonic circulations south of the Kuroshio Extension. Furthermore, 20%–30% of the observed STMW pycnostads have two or three potential vorticity minima, mostly near temperatures of 16.6° and 17.7°C. The authors presume that such a structure formed as a result of the interleaving of the 16.6° and 17.7°C STMWs after they are stirred by mesoscale circulations, following which they are vertically mixed to form the 17.2°C STMW observed in late fall. These results indicate the importance of horizontal processes in destroying the vertically uniform structure of STMW after spring, particularly when the Kuroshio Extension is in a variable state.

scholarly journals Southward spreading of the Fukushima-derived radiocesium across the Kuroshio Extension in the North Pacific

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Yuichiro Kumamoto ◽  
Michio Aoyama ◽  
Yasunori Hamajima ◽  
Tatsuo Aono ◽  
Shinya Kouketsu ◽  
...  
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

scholarly journals Winter Extreme Flux Events in the Kuroshio and Gulf Stream Extension Regions and Relationship with Modes of North Pacific and Atlantic Variability

2015 ◽  
Vol 28 (12) ◽  
pp. 4950-4970 ◽  
Author(s):  
Xiaohui Ma ◽  
Ping Chang ◽  
R. Saravanan ◽  
Dexing Wu ◽  
Xiaopei Lin ◽  
...  
Keyword(s):  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Propagation Path ◽  
Northwestern Pacific ◽  
Boreal Winter ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Boreal winter (November–March) extreme flux events in the Kuroshio Extension region (KER) of the northwestern Pacific and the Gulf Stream region (GSR) of the northwestern Atlantic are analyzed and compared, based on NCEP Climate Forecast System Reanalysis (CFSR), NCEP–NCAR reanalysis, and NOAA Twentieth Century Reanalysis data, as well as the observationally derived OAFlux dataset. These extreme flux events, most of which last less than 3 days, are characterized by cold air outbreaks (CAOs) with an anomalous northerly wind that brings cold and dry air from the Eurasian and North American continents to the KER and GSR, respectively. A close relationship between the extreme flux events over KER (GSR) and the Aleutian low pattern (ALP) [east Atlantic pattern (EAP)] is found with more frequent occurrence of the extreme flux events during a positive ALP (EAP) phase and vice versa. A further lag-composite analysis suggests that the ALP (EAP) is associated with accumulated effects of the synoptic winter storms accompanied by the extreme flux events and shows that the event-day storms tend to have a preferred southeastward propagation path over the North Pacific (Atlantic), potentially contributing to the southward shift of the storm track over the eastern North Pacific (Atlantic) basin during the ALP (EAP) positive phase. Finally, lag-regression analyses indicate a potential positive influence of sea surface temperature (SST) anomalies along the KER (GSR) on the development of the extreme flux events in the North Pacific (Atlantic).

Variation of Surface Radiocarbon in the North Pacific During Summer Season 2004–2016

Radiocarbon ◽  
2019 ◽  
Vol 61 (5) ◽  
pp. 1367-1375 ◽  
Author(s):  
T Aramaki ◽  
S Nakaoka ◽  
Y Terao ◽  
S Kushibashi ◽  
T Kobayashi ◽  
...  
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
Deep Convection ◽  
Subtropical Region ◽  
Subarctic Region ◽  
Surface Ocean ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

ABSTRACTSurface radiocarbon (Δ14C) in the North Pacific has been monitored using a commercial volunteer observation ship since the early 2000s. Here we report the temporal and spatial variations in Δ14C in the summer surface water when the surface ocean is vertically stratified over a 13-yr period, 2004–2016. The long-term Δ14C decreasing trend after the late 1970s in the subtropical region has continued to the present and the rate of decrease of the Kuroshio and Kuroshio Extension, North Pacific and California current areas is calculated to be –3.3, –5.2 and –3.3 ‰/yr, respectively. After 2012 the Δ14C of the Kuroshio and Kuroshio Extension area, however, has remained at an approximately constant value of around 50‰. The result may indicate that subtropical surface Δ14C in the western North Pacific has reached an equilibrium with atmospheric Δ14CO2. The Δ14C in the subarctic region is markedly lower than values in the subtropical region and it seems that the decreasing tendency of surface Δ14C has changed to an increasing tendency after 2010. The results may indicate that bomb-produced 14C, which has accumulated below the mixed layer in the past few decades, has been entrained into the surface layer by deep convection.

scholarly journals Western Boundary Currents and Frontal Air–Sea Interaction: Gulf Stream and Kuroshio Extension

2010 ◽  
Vol 23 (21) ◽  
pp. 5644-5667 ◽  
Author(s):  
Kathryn A. Kelly ◽  
R. Justin Small ◽  
R. M. Samelson ◽  
Bo Qiu ◽  
Terrence M. Joyce ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Western Boundary ◽  
Mode Water ◽  
The North ◽  
The North Atlantic ◽  
Current Systems ◽  
The North Pacific

Abstract In the Northern Hemisphere midlatitude western boundary current (WBC) systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean. Their potential contribution to the climate system motivated major parallel field programs in both the North Pacific [Kuroshio Extension System Study (KESS)] and the North Atlantic [Climate Variability and Predictability (CLIVAR) Mode Water Dynamics Experiment (CLIMODE)], and preliminary observations and analyses from these programs highlight that complexity. The Gulf Stream (GS) in the North Atlantic and the Kuroshio Extension (KE) in the North Pacific have broad similarities, as subtropical gyre WBCs, but they also have significant differences, which affect the regional air–sea exchange processes and their larger-scale interactions. The 15-yr satellite altimeter data record, which provides a rich source of information, is combined here with the longer historical record from in situ data to describe and compare the current systems. While many important similarities have been noted on the dynamic and thermodynamic aspects of the time-varying GS and KE, some not-so-subtle differences exist in current variability, mode water properties, and recirculation gyre structure. This paper provides a comprehensive comparison of these two current systems from both dynamical and thermodynamical perspectives with the goal of developing and evaluating hypotheses about the physics underlying the observed differences, and exploring the WBC’s potential to influence midlatitude sea–air interaction. Differences between the GS and KE systems offer opportunities to compare the dominant processes and thereby to advance understanding of their role in the climate system.

scholarly journals Energetics of Eddy–Mean Flow Interactions along the Western Boundary Currents in the North Pacific

2019 ◽  
Vol 49 (3) ◽  
pp. 789-810 ◽  
Author(s):  
Xiaomei Yan ◽  
Dujuan Kang ◽  
Enrique N. Curchitser ◽  
Chongguang Pang
Keyword(s):  
Kinetic Energy ◽  
Western Boundary ◽  
Mean Flow ◽  
Boundary Currents ◽  
The North ◽  
Flow Interactions ◽  
The Mean ◽  
Eddy Field ◽  
The Kuroshio ◽  
The North Pacific

AbstractThe energetics of eddy–mean flow interactions along two western boundary currents of the North Pacific, the Kuroshio and Ryukyu Currents, are systematically investigated using 22 years of numerical data from the Ocean General Circulation Model for the Earth Simulator (OFES). For the time-mean and time-varying flow fields, all the energy components and conversions exhibit inhomogeneous spatial distributions. In the two currents, complex cross-stream and along-stream variations are seen in the eddy–mean flow energy conversions. East of Taiwan, the kinetic energy is mainly transferred from the mean flow to the eddy field through barotropic instability, whereas the baroclinic energy conversions form a meridional dipole structure caused by the topographic constraint. In the northern area, particularly, the eddy field drains 2.25 × 108 W of kinetic energy and releases 2.82 × 108 W of available potential energy when interacting with the mean flow, indicating that mesoscale eddies impinging on the Kuroshio decay with baroclinic inverse energy cascades. In the Ryukyu Current, inverse energy conversions from the eddy field to the mean flow also dominate the power transfer in the subsurface layer. The eddy field transfers 0.16 × 108 W of kinetic energy and 1.89 × 108 W of available potential energy to the mean flow, suggesting that meososcale eddies play an important role in maintaining the velocity and hydrographic structure of the current. In other areas, both barotropic and baroclinic instabilities contribute to the generation of eddy kinetic energy with the latter one providing more than 3 times as much power as the former one.

scholarly journals Sensitivity of the Ventilation Process in the North Pacific to Eddy-Induced Tracer Transport*

2006 ◽  
Vol 36 (10) ◽  
pp. 1895-1911 ◽  
Author(s):  
Takahiro Endoh ◽  
Yanli Jia ◽  
Kelvin J. Richards
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Kuroshio Extension ◽  
Tracer Transport ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Subduction Rate ◽  
The Kuroshio ◽  
The North Pacific

Abstract A coarse-resolution isopycnal model coupled with a bulk mixed layer model is used to examine the effect of isopycnal thickness diffusion, which parameterizes the subgrid-scale eddy-induced tracer transport, on ventilation of the North Pacific Ocean. Three numerical experiments with thickness diffusivities of 0 m2 s−1 and around 500 and 2000 m2 s−1 are carried out. The model successfully reproduces a deep winter mixed layer in the subarctic North Pacific, leading to well-formed mode waters and the subtropical countercurrent in the experiment with thickness diffusivity around 500 m2 s−1. The annual-mean subduction rate has peaks at densities of 25.0–25.4 and 26.4 σθ. The former peak spans the densities of North Pacific Subtropical Mode Water and North Pacific Eastern Subtropical Mode Water, whereas the latter peak is centered near the density of North Pacific Central Mode Water. The annual mean obduction rate also has the former peak and a slight enhancement corresponding to the latter peak. The Kuroshio plays a crucial role in obduction of North Pacific Subtropical Mode Water by transferring it northward from the permanent pycnocline to the seasonal pycnocline around the Kuroshio Extension, the importance of which has been overlooked in previous studies. In contrast to the simple expectation that the eddy-induced tracer transport enhances the ventilation process, stronger circulation with lower thickness diffusion increases the annual-mean subduction rate by carrying the subducted water quickly away from the seasonal pycnocline into the permanent pycnocline, as well as the annual-mean obduction rate by transferring much water from the permanent pycnocline to the seasonal pycnocline. As thickness diffusivity increases, the former peaks in the subduction and obduction rates occur at lighter densities, whereas the latter peak in the subduction rate is shifted toward higher densities.

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